Option A (simpler)

Drag and drop placeholder citations into Scrivener, using the footnotes pane (create the empty footnote first)

Note: these will only bring the main part of the citation, you’ll need to add page numbers manually. For example change this: {Longford, 2006} to this: {Longford, 2006, 10-14}

Compile or export from Scrivener as an RTF file

Process the file in Zotero (cog wheel -> RTF Scan…)

Open the new version of the file in Word and you should have properly formatted footnotes and a bibliography

Option B

The main downside of Option A is that it does not maintain a live connection to your Zotero library. Once you process the RTF file, the footnotes and bibliography are essentially plain text, not connected to your Zotero database. But this is probably fine if you prefer to work on your text inside Scrivener, and only export and process the footnotes when you are finished. Any changes could then be made to the Scrivener version and processed again.

If you prefer to maintain the live connection to your Zotero library, including allowing for the reverse process, you can download the RTF/ODF-Scan plugin for Zotero. Adding citations to Scrivener works similarly to Option A. But, instead of exporting as an RTF file, you will need to export as an ODT file. Then you can process the file in Zotero as before.

One other key difference: you will need to open and work with the processed document using a Microsoft Word alternative, either LibreOffice or OpenOffice. You should now have a document with footnotes -and- a live connection allowing you to change/reformat them via Zotero.